In a diesel engine, a DPF is provided in an exhaust pipe line so as to reduce PM included in an exhaust gas. The DPF traps PM such as soot included in an exhaust gas and discharges the exhaust gas of which the PM is reduced to external air. When the PM trapped by the DPF increases in amount, a filter function degrades. For this reason, the DPF is regenerated by burning the trapped PM. The regeneration includes natural regeneration in which the deposited PM is naturally burned when the temperature of the exhaust gas is high and forced regeneration which is performed when a PM deposition amount exceeds a predetermined reference value. In the forced regeneration, the engine operation state is adjusted so as to increase the exhaust gas temperature and external dosing for injecting a fuel at the front stage of the DPF or internal dosing for injecting a fuel into a cylinder of the engine is performed so as to forcedly burn the PM. The forced regeneration further includes automatic forced regeneration and manual forced regeneration. When there is a possibility that the DPF may be blocked due to the PM deposition amount which becomes larger than a reference value in the automatic forced regeneration, an alarm for prompting the execution of the manual forced regeneration is notified to a driver.
Here, since the PM deposition amount of the PM trapped in the DPF may not be actually measured during the operation of the engine, the PM deposition amount is calculated by the estimation. For example, Patent Literature 1 discloses a DPF deposition amount estimation device that includes a PM discharge amount model of which a PM discharge amount is set by an engine operation state, a PM regeneration amount model of which a PM regeneration amount is set by a temperature difference between an outlet temperature and an inlet temperature of a DPF, and a DPF differential pressure model of which a PM deposition amount is set from an exhaust gas flow rate and a differential pressure of the DPF and calculates a PM deposition estimation amount of the DPF by adding a PM deposition correction amount correcting an estimation value of the DPF differential pressure model using a coefficient K set in accordance with an engine speed and an engine fuel injection amount to a difference between the PM discharge amount and the PM regeneration amount.
Further, Patent Literature 2 discloses an exhaust gas purification system which obtains a time change rate of a PM production amount using a PM production amount estimation model equation as a mathematical model calculating the PM production amount from an engine speed, a fuel flow rate, and a DPF differential pressure change rate as a time change rate of a differential pressure before and after a DPF, obtains a time change rate of a PM purification amount using a PM purification amount estimation model equation of a mathematical model calculating the PM purification amount, and estimates a PM accumulation amount of the DPF from the time change rate of the PM production amount, the time change rate of the PM purification amount, and the trapping rate of the DPF.